Method and system for performing a batch reverse osmosis process using a tank with a movable partition

ABSTRACT

A reverse osmosis system and method of operating the same includes a membrane housing comprising a reverse osmosis membrane therein. The membrane housing has a feed fluid input, a brine outlet and a permeate outlet; The system further includes a charge pump, a plurality of valves and a tank having a volume comprising a movable partition dividing the volume into a first volume and a second volume. The plurality of valves selectively couples the charge pump to the first volume or the second volume and the brine outlet to the second volume or the first volume respectively.

RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.15/783,184, filed Oct. 13, 2017 and claims benefit to U.S. ProvisionalApplication 62/409,021, filed Oct. 17, 2016, the disclosures of whichare incorporated by reference herein.

TECHNICAL FIELD

The present disclosure relates generally to reverse osmosis systems,and, more specifically, to a method and system for using separatesvolumes to enable a continuous process.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Reverse osmosis systems typically use one or more membrane housings thathave one or more membranes therein that are used to extract anessentially pure fluid from a solution. The desalination reverse osmosismembranes receive feed fluid from brackish or sea water and extractfresh water therefrom. Fresh water is extracted or separated when thepressure of the feed fluid exceeds the osmotic pressure of the fluidwhich allows permeate or product fluid to cross the semi-permeablereverse osmosis membrane. The fluid that is left on the input side tothe membrane becomes higher in salt concentration because fresh waterthat travels through the membrane does not include the salt. The waterthat passes through the membrane is referred to as a permeate. Thepressure required to produce fresh water is proportional to theconcentration of the total dissolved solids (TDS) in this feed solutionwithin the reverse osmosis housing. For typical ocean water, theconcentration is about 35,000 parts per million (ppm) and thecorresponding osmotic pressure is about 450 pounds per square inch (psi)(3,102 kPa). For 70,000 ppm feed fluid, the osmotic pressureapproximately doubles to 900 psi (about 6,205 kPa). A typical seawaterreverse osmosis system uses a series of membranes that recover up toabout 45% of the fresh water and generate about 55% concentrate brinefrom the original volume of seawater. The net driving pressure (NDP)equals the feed pressure minus the osmotic pressure. The net drivingpressure is the pressure energy available to drive pure fluid across themembrane.

Referring now to FIG. 1, a membrane channel 10 is illustrated betweentwo membrane sheets 12. The channel 10 includes an inlet 14 and anoutlet 16. An amount of permeate 18 represented by the droplets haspermeated from the channel 10 through the membrane sheets 12. As thefeed fluid that enters the inlet 14 and progresses through the membranechannel 10, the concentration of dissolved solids increases as thepermeate 18 is extracted. The higher number of droplets of permeate 18toward the inlet 14 indicate that permeate production is higher towardthe inlet 14 and decreases toward the outlet 16. Because of theincreasing totaled dissolved solids and the corresponding reduction inthe net driving pressure, less permeate is extracted from the channel10.

Referring now to FIG. 2, the relationship of the feed pressure, osmoticpressure, the feed total dissolved solids, the permeate rate and the netdriving pressure is illustrated for a membrane channel of a reverseosmosis system with about 45% recovery handling of the seawater. As isillustrated, the feed pressure is about 860 psi (5929 kPa) and losesabout 10 psi (69 kPa) over the life of the channel. The osmotic pressureat the start of the channel is about 450 psi (3,100 kPa) and rises toabout 820 psi (5653 kPa) due to the increase in total dissolved solid ofthe feed. The feed total dissolved solid begins at about 35,000 ppm andrises to about 63,000 ppm at the end of the channel. The net drivingpressure begins at about 500 psi (3450 kPa) and decreases to about 50psi (350 kPa). The permeate flow rate decreases to negligible at the endof the channel 10.

Referring now to FIG. 3, a batch reverse osmosis system 30 isillustrated. The batch reverse osmosis system 30 is used to treat avolume of feed fluid. The process repeatedly passes an initial volume offeed fluid through the reverse osmosis membranes and removes permeateuntil a desired level of concentration of total dissolved solids or aspecific amount of permeate has been produced. The batch reverse osmosissystem 30 has a feed reservoir or source 32 that communicates fluid to acharge pump 34. The charge pump 34 communicates fluid through a valve 36and into an inlet 38 of a tank 40. The valve 36 is open during fillingof a batch tank 40 and is closed after the tank 40 is filled with feedfluid. The tank 40 may include an air vent 41 for releasing displacedair as the tank 40 is filled and drawing in air as the tank 40 isemptied. A drain valve 42 is coupled to a port 44 for draining theprocessed fluid into a brine tank 46 as will be described in more detailbelow.

An outlet port 50 communicates fluid from the tank 40 to a high pressurepump 52 through pipes 51 and 53. The high pressure pump 52 increases thepressure of the fluid from the tank 40 and communicates the fluid to themembrane housing 54 that has a membrane 56 therein. A permeate pipe 58drains permeate that passes through the membrane 56. The permeate pipe58 is in communication with a permeate tank 60 that collects thepermeate that passes therethrough. A brine pipe 62 communicates brineconcentrated fluid through a valve 64 to a port 66 in the tank 40.

A controller 70 coupled to a concentration sensor 72 monitors theprocess and the concentration of the fluid within the tank 40 to end theprocess when the fluid within the tank 40 reaches a predeterminedconcentration. The controller 70 may also be used to control the variousvalves including valve 36, the valve 64 and the pumps including the highpressure pump 52 and the charge pump 34. In the process, feed fluid isprovided to the tank 40 through the charge pump 34 and open valve 36.When the tank 40 is filled, the charge pump 34 is powered off and thevalve 36 is closed. As the tank 40 is filling, air is vented from thetank through the air vent 41. Drain valve 42 is also closed during thefilling of the tank 40 through pipe 38. During batch processing, thehigh pressure pump 52 is controlled to provide pressure. The valve 64 isalso opened during batch processing to circulate the concentrated brineback to the tank 40. During batch processing, fluid from the tank 40leaves the port 50 and enters the pipe 51 whereby the high pressure pump52 increases the pressure and provides the desired pressure to themembrane housing 54 through pipe 53. Permeate exits the membrane housingthrough the pipe 58. The control valve 64 is adjusted to achieve adesired flow rate and depressurized brine fluid returns to the tank 40through port 66.

As the batch of fluid within the tank is processed, concentrated brineis recirculated back to the tank 40 which increases the concentration ofthe fluid within the tank 40. As the fluid becomes increasinglyconcentrated, the pressure output by the high pressure pump 52 isincreased. The recirculation of the fluid from the tank 40 to the highpressure pump 52 through the membrane housing 54, brine pipe 62 and thevalve 64 continues until the sensor 72 measures the endingconcentration.

Once the desired concentration has been achieved, the high pressure pump52 is stopped and the concentrate within the tank 40 is drained throughthe drain valve 42 which is opened to drain the fluid into the brinetank 46. Thereafter, the drain valve 42 is closed and the charge pump 34is activated and the valve 36 is open to provide a fresh batch of feedfluid to the tank 40.

Referring now to FIG. 4, another prior reverse osmosis system 30′ isillustrated in further detail. The same components illustrated in FIG. 3are provided with the same reference numerals. In this example, anenergy recovery device such as a turbocharger 74 having a turbineportion 74T and a pump portion 74P is used to recover at least a portionof the energy of the pressurized brine concentrate stream in the brineoutlet pipe 62. That is, the brine from the membrane housing 54 iscommunicated to the turbine portion 74T of the turbocharger 74. Theturbine 74T rotates the pump portion 74P to increase the pressure withinthe input line 78 to the membrane housing 54. The depressurized brinefluid returns to the tank 40 through the inlet port 66 and the valve 64.The high pressure pump 52 can operate at a lower pressure because of theboost provided by the turbocharger 74. By reducing the pump power, theadded heat into the fluid is reduced. This also eliminates coolingequipment to maintain the fluid temperature to a desired batchtemperature.

Referring now to FIG. 5, a similar example to that illustrated in FIG. 3is set forth. In this example, another high pressure pump 80 is coupledbetween the fill reservoir 32 and the input port 38 to the tank 40. Thisconfiguration may be referred to as a “semi-batch” reverse osmosissystem 30″. In this example, the charge pump 34 transfers feed fluidfrom the reservoir 32 to entirely fill the tank 40. The valve 36 isclosed. The high pressure pump 80 is used to pump feed into the fluidtank 40 from the reservoir 32. The pump 52 is engaged so that as feed isinjected into the tank 40 through the feed pipe 51 and the feed fluidinput pipe 53, the pressure quickly rises due to the incompressibilityof the fluid. The pressure reaches the point where the permeate exitsthe membrane housing 54 through the permeate outlet pipe 58 into thetank 60. The permeate flow equals the rate of flow from the highpressure pump 80. As permeate is extracted, the pressure in tank 40increase to overcome the increasing osmotic pressure in order tomaintain the permeate flow into the permeate tank 60. The pump 52circulates fluid from the tank 40 through the membrane housing 54 andback to the tank 40. Concentration sensor 72 senses the concentration ofthe fluid within the tank 40 and when a concentration has reached aconcentration limit, the high pressure pump 80 is shut down and valve 42is opened to allow the fluid within the tank 40 to drain into the brinetank 46. The next batch begins by opening the valve 36 and increasingthe amount of fluid within the tank 40 until it is full wherein thevalve 36 is closed and the high pressure pump 80 is activated to feedfluid into the tank 40 during the permeate production as describedabove.

SUMMARY

The present disclosure provides a method and system for batch processingfeed fluid in a system that can continuously operate in an efficientmanner.

In one aspect of the disclosure, a reverse osmosis system and method ofoperating the same includes a membrane housing comprising a reverseosmosis membrane therein. The membrane housing has a feed fluid input, abrine outlet and a permeate outlet; The system further includes a chargepump, a plurality of valves and a tank having a volume comprising amovable partition dividing the volume into a first volume and a secondvolume. The plurality of valves selectively couples the charge pump tothe first volume or the second volume and the brine outlet to the secondvolume or the first volume respectively.

In another aspect of the disclosure, a method includes filling a firstvolume and a second volume of a tank, having a movable partitionseparating the first volume at a first end of the tank and the secondvolume at a second end of the tank, producing permeate with fluid in thesecond volume at a membrane housing, recirculating brine to the secondvolume from the membrane housing, and filling the first volume with feedfluid in response to producing permeate to cause the partition to movetoward the second end until a concentration of fluid in the secondvolume exceeds a threshold.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is a cutaway view of a membrane and fluid flow therethroughaccording to the prior art.

FIG. 2 is a chart of feed pressure, osmotic pressure, feed totaldissolved solids (TDS), permeate rate and net driving pressure (NDP)according to the prior art.

FIG. 3 is a schematic view of a reverse osmosis system according to thebatch-operated reverse osmosis system according to the prior art.

FIG. 4 is a second schematic view of a batch operated system accordingto the prior art.

FIG. 5 is a schematic of a third batch-operated system according to theprior art.

FIG. 6 is a schematic of a batch-operated system according to thedisclosure.

FIG. 7 is a state chart for the operating states of the valves of FIG. 6during operation.

FIG. 8A is an alternative valve configuration for a reverse osmosissystem.

FIGS. 8B and 8C illustrate the different states of the spool valve ofFIG. 8A.

FIG. 9 is a state table for the operating states of the reverse osmosissystem using the spool valve of FIG. 8A.

FIG. 10 is an alternative example of a tank and movable partition.

FIG. 11 is a side view of an alternative configuration for the movablepartition of FIG. 10.

FIG. 12 is a chart illustrating feed pressure, osmotic pressure, feedtotal dissolved solids, permeate rate and net driving pressure accordingto the operation of the present examples.

FIG. 13 is a schematic view of another example of a reverse osmosissystem of the disclosure.

FIG. 14A is a partial schematic view of the reverse osmosis system ofFIG. 13 in a first state.

FIG. 14B is a partial schematic view of the reverse osmosis system ofFIG. 13 in a second state.

FIG. 15A is a partial schematic view of the reverse osmosis systemhaving a common wall.

FIG. 15B is a top view of the reverse osmosis tank of FIG. 15A.

FIG. 15C is an alternative example of a common wall tank.

FIG. 16 is a side view of an in-water reverse osmosis tank system.

FIG. 17 is a side view of an on-land reverse osmosis tank system.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses. Forpurposes of clarity, the same reference numbers will be used in thedrawings to identify similar elements. As used herein, the phrase atleast one of A, B, and C should be construed to mean a logical (A or Bor C), using a non-exclusive logical or. It should be understood thatsteps within a method may be executed in different order withoutaltering the principles of the present disclosure.

In the following description, a method and system for managing thereverse osmosis system to minimize energy consumption of the highpressure pump is set forth. A process that achieves continuous operationby allowing recharge of fresh feed to occur while the batch process isprocessing permeate is set forth.

Referring now to FIG. 6, the same elements are provided with the samereference numerals from those of FIGS. 1 through 5. In this example, thetank 40 includes a movable partition 610. The movable partition 610divides the volume of the tank into a first volume 612 and a secondvolume 614. The movable partition 610 may separate the volumes 612 and614 so that there is no mixing of fluid therebetween. That is, duringthe process, different salt concentrations may be with the first volume612 and the second volume 614. The tank 40 has a first end 616 and asecond end 618. The first end 616 helps define the first volume 612. Thesecond end 618 helps define the second volume 614. A side wall 619,together with the first end 616 and the second end 618, define theentire volume within the tank 40. The tank 40 may also be variousshapes. The movable partition 610 moves up and down during permeateproduction process. Details of this will be described below. A three-wayvalve 620 is used in place of the valve 36. The three-way valvecommunicates fluid from the feed source 32 received at port 620C and thecharge pump 34 to either the first port 622 or the second port 624 ofthe tank 40 through valve port 620A or 620B, respectively. The valveport 620A is in communication with the port 622. The port 620B is incommunication with the port 624 of the tank 40. Feed fluid is thuscommunicated into the first volume 612 through the port 622. Fluid iscommunicated into the second volume 614 through the port 624.

Another three-way valve 630 has a valve port 630A, a valve port 630B anda port 630C. The port 630C is in communication with the high pressurepump 52 and a brine drain valve 632. The brine drain valve 632 is incommunication with orifices 634 and the brine reservoir 638. A totaldissolved solid sensor or concentration sensor 635 may monitor theconcentration of the drain or brine fluid entering the brine reservoir638.

Another three-way valve 640 has a port 640C in communication with thebrine pipe 62, a port 640B that is in communication with the port 642(that is in communication with the first volume 612 of the tank 40) anda port 640A in communication with the port 644 which is in communicationwith the second volume 614 of the tank 40.

Referring now to FIGS. 6 and 7, the operation of the reverse osmosissystem 30″ is set forth. The states of the valves 620, 630, 632 and 640are set forth. The fluid in the three-way valves flows into or out ofthe port “C” and into or out of one of the port “A” or port “B” for eachvalve which are denoted in the chart below. Valve 632 is a two-way valvethat is either opened (“O”) or closed (“C”). In the first state, the ROsystem 30″ makes permeate at the membrane housing 54 by way of the pipe58. The valves 620, 630, 632 and 640 may be referred to as a pluralityof valves. However, the various states of the valves may allow variousconditions. In the first state, the plurality of valves are set to makepermeate from the volume 614 while feed fluid enters the volume 612.That is, the valve 620 is set to communicate feed fluid from the port620C to 620A and into the port 622. It is presumed in state 1 that thetank 40 is already filled with fluid. Fluid is provided from the port644 to valve 630 and, in particular, to port 630B of the valve 630.Fluid is communicated through the valve and port 630C to the highpressure pump 52 and membrane housing 54 where permeate is producedthrough the pipe 58. Leftover brine fluid from the process in themembrane housing 54 returns to the tank though the pipe 62 and port 640Cand port 640A of the three-way valve 640. Fluid leaves the port 640A ofthe valve and enters the port 644 in the second end 618 of the tank 40.During this process, the valve 632 is closed. As the process progresses,the movable partition 610 moves in a direction toward the second end 618or, in this example, in a downward direction. When the concentration ofthe fluid in the volume 614 reaches a predetermined concentration asdetermined by the controller 70 using the concentration sensor 72A, theprocess stops processing permeate from the volume 614 and purges brinefluid from the volume 614.

When brine is being purged from the volume 614, the system enters state2, the valve states of the valves 620, 630 and 640 in state 2 areidentical to those of state 1 with the exception of valve 632 whichchanges from closed to open. When valve 632 opens, brine continues to bepumped through the pipe 51, the high pressure pump 52, pipe 53 and thevalve 632. Ultimately, the movable partition 610 moves in a downwarddirection at or near the second end 618.

In state 3 of FIG. 7, the valve states of valve 620, 630 and 640 arereversed from that of state 1. That is, valve 620 now communicates fluidfrom the port 620C through the port 620B and into the port 624 of thetank 40. Valve 630 communicates fluid from the port 642 through the port630A and 630C of the three-way valve 630 to the pipe 51. Valve 640communicates brine from the port 640C through the port 640A. Valve 632is in a closed state and thus all of the fluid passing through the valve630 enters the high pressure pump 52 and the membrane housing 54.

In state 4, brine is purged from the first volume 612. In thissituation, the plurality of valves 620, 630 and 640 are in the identicalstate as that of state 3 with the exception being valve 632 which isplaced in an open state. In state 3, the movable partition 610 movestoward the first end 616 until the sensor 72B senses a predeterminedconcentration of the first volume by way of the controller 70. Thecontroller 70 then changes the state of the various valves and maychange the speed of the high pressure pump 52 and the pump 34.

A few notable features set forth in FIG. 6 may be evident to thoseskilled in the art. Even though purging through the valve 632 takesplace, when purging either the volume 612 or the volume 614, themembrane housing 54 continues to receive fluid through pipe 11, pump 52and pipe 53 and generates permeate fluid through the permeate pipe 58.

During the process, the flow rate through the membrane housing 54 ascontrolled by the high pressure 52 is optimized to prevent fouling andmaximize membrane efficiency. The pump 34 continues to replace thepermeate within the appropriate volume of the tank 40.

The orifices 634 reduce the pressure drop across the valve to maximizethe valve life and to allow the brine drain to drain until the partitionhas reached the bottom of the tank in state 1. The flow resistancethrough the valve 632 allows enough resistance so that some permeateproduction is performed. That is, not all of the circulated brine fluidleaves the system but rather a portion of the circulating brine fluidreaches the membrane housing 54 through the pump 52. After state 2 andprior to state 3, the pipes 51, 53 and 62 between the various componentsare preferably kept to a small distance so the amount of dead volume ofhighly concentrated brine between the transition from states 1 and 2 tostates 3 and 4 is reduced to a minimum.

Reducing the amount of brine in the dead volume of some configurationsmay also be important.

Referring now to FIG. 8A, a spool valve 810 is used to replace thevalves 620, 630 and 640 illustrated above in FIG. 6 in the reverseosmosis system 30 iv. The spool valve 810 is in fluid communication withthe charge pump 34, the brine pipe 62, the high pressure pump 52 and thedrain valve 632.

The spool valve 810 has a linear actuator 812 that is used to move a rod814 to align the spool disks 816, 818 and 820 to their desired positionrelative to the various ports 830-844 formed in the casing 850 of thespool valve 810.

It should be noted that the illustration set forth in FIG. 8A do notinclude the controller 70 and the electrical couplings to the variouspumps and to the sensors 72A, 72B and 635. However, the sensors may alsobe provided in FIG. 8 in the same manner as FIG. 6.

In this configuration, the linear actuator 812 is disposed in theleftmost or most outward position away from the actuator 812 position.It should also be noted that a seal 860 is disposed between the port 834and the port 842. By providing the seal 860, the high pressure portionend or portion and the low pressure end or portion within the spoolvalve 810 are separated. By alignment of the disks 816, 818 and 820,different flow paths may be formed through the casing so that fluid maybe provided to and from the various devices in a similar manner to thatset forth in FIG. 6. FIGS. 8B and 8C illustrate state A which alsocorresponds to FIG. 8A and state B which corresponds to the disks 816,818 and 820 moved to the rightmost position or toward linear activity812 with the rod 814.

Effectively, ports 830, 838 and 832 act in a fluidically similar mannerto three-way valve 620. The ports 832, 838 and 840 act in a fluidicallysimilar manner to valve 630 and ports 842, 844 and 836 act in afluidically similar way to valve 640.

Referring now to FIGS. 8A-8C and FIG. 9, the various states are setforth using the spool valve. In state A, permeate is made from thevolume 614. Feed fluid enters volume 612. The movable partition 610moves in a downward position during permeate production in state A.Valve 632 is closed in state 1. State A corresponds to the rod 814 beingin the leftmost position. That is, state A corresponds to fluid beingcommunicated between ports 838 and 832, between ports 840 and 834 andbetween ports 844 and 836. State 2 has the spool valve 810 also in stateA. That is, brine is being purged from the volume 614 while feed fluidcontinues to reach the membrane housing 54. Pump 52 continues tooperate. Valve 632 in state 2 is in an open position.

In state 3, permeate is being made from volume 612 and feed fluid isentering volume 614. In state B, fluid is being communicated betweenports 830 and 838, between ports 832 and 840 and between ports 842 and836. As noted above, during the process of permeate production, the pump52 may be controlled to increase in speed and therefore provide higherpressure to the membrane housing 54.

Referring now to FIG. 10, the movable partition 610 illustrated abovemay be a conformable movable partition 610′ as illustrated in FIGS. 10and 11. The movable partition 610′ includes an upper surface 1010 and alower surface 1012. The upper surface 1010 partially defines the firstvolume 612 of FIG. 6. The lower surface 1012 partially defines thesecond volume 614. The upper surface 1010 conforms to the shape of thefirst end 616 of tank 40. The shape of the lower surface 1012 conformsto the shape of the second end 618 of tank 40. This allows aminimization (or near elimination) of the volume 612 or 614 near the endof the process. It should be noted that the pressure difference betweenthe upper surface 1010 and the lower surface 1012 is very minimal andthus the cost of preventing leakage around the movable partition 610′ isminimal. A seal 1020 may be disposed around the movable partition 610′.A plurality of different types and shapes and numbers of seals 1020 maybe provided.

Referring specifically to FIG. 11, the movable partition 610′ mayinclude a passage 1110 therethrough. The passage 1110 has a width 1112that is wider than both of the difference between the ports 622 and 642and ports 624 and 644. The width of the passage is defined at referencenumber 1112. A swinging plate 1120 may have a spring loaded pivot 1122coupled thereto. The spring force allows the swinging plate 1120 to openonly under high pressures experienced at the end of each permeateproduction cycle. The open position of the swinging plate 1120 ismaintained until feed fluid is pumped into the tank volume and thedirection of flow through the swinging plate 1120 is reversed (or thedrain valve is closed). In both instance, the pressure is relieved.After relieving the pressure and the permeate production begins with thevolume on the opposite side of the opening of the swinging plate 1120.The plate 1120, because it is in axial alignment with the port 622, 642,624 and 644, allows the plate 1120 the move in the direction indicatedby the arrows under high pressure. When the partition 610 moves up ordown within the tank 40, the plate 1120 will remain in a closed positionto prevent mixing of the volumes 612 and 614. Because there is still a“dead” volume within the pipes attached to the membrane and variouspumps, feed flow continues to enter the tank and causes the partition toopen under the force of the feed flow. By allowing the plate 1120 toopen, some of the feed flow is able to enter the piping to flush thepipes. Thus, the highly concentrated brine is removed from the pipes andthe dead volume within the pipes is eliminated. A total dissolved solidsensor 635 illustrated in FIG. 6 may be used to end the fluid flowthrough the plate 1120 and thus the permeate production can be resumedas the partition moves in the opposition direction. Thus, the plate 1120will open at the bottom of the tank 40 until the TDS sensor 635 readsthat a drain fluid concentration is below a drain concentrationthreshold which corresponds to a low amount of total dissolved solidspresent in feed fluid in contrast to high TDS fluid present at the endof permeate production. The sensor 635 senses the transition between theTDS amounts. Then, the plurality of valves may be changed so that feedfluid enters the bottom of the tank and permeate production is fromvolume 612. Likewise, when the movable partition 610′ reaches the toplimit of travel, the swinging plate 1120 may open and flush the pipinguntil the TDS sensor 635 reads below a drain fluid concentrationthreshold. Thereafter, the plurality of the valves may change state andfeed fluid provided into the volume 612 so that permeate is producedusing the volume 614.

Referring now to FIG. 12, the conditions during a batch operated runusing the partition 610′ illustrated above is set forth. As can be seen,compared to that of FIG. 2, the net driving pressure and permeate rateare relatively constant until the time between the finish and the purge.This time is relatively small and thereafter the cycle starts in thereverse direction.

By providing the partitions 610 or 610′, the incoming feed fluid doesnot mix with the brine. This is different than the known semi-batchsystem described above in FIGS. 1-5. The elimination of the feed fluidand the brine mixing increases the efficiency of the overall system bypreventing irreversible losses with different levels of total dissolvedsolids. Further, there is no disruption to the membrane production torecharge the tank after the brine has been fully processed because thetank is already charged with fresh feed on the other side of the movablepartition 610 or 610′ with purging of the dead volume not interruptingpermeate production. The permeate production at a constant ratecontinues until the purge process is complete even though the process isat a slightly lower efficiency. The process only takes a short amount oftime and full permeate production is then continued. Although the systemundergoes a range of pressures in response to the degree of brineconcentration, full depressurization is never performed. This reducesthe cyclical stresses on the tank, piping and the membrane.

Referring now to FIG. 13, a reverse osmosis system 30 ^(v) in thisexample, two tanks 40A and 40B are used to house the first volume 612and a second volume 614 rather than having the volumes divided by themovable partition 610 as illustrated above. By providing two differentvolumes, relatively low cost equipment and high maximum energyefficiency may be achieved. When using the movable partition or twoseparate tanks, the fluid being processed is not allowed to mix with thepreviously processed brine and therefore the total dissolved solids inthe feed are minimized. The same reference numerals for each of thecomponents set forth previously are used in FIGS. 13, 14A and 14B. Inaddition to two separate volumes and two tanks 40A, 40B, two separateconcentration sensors 1330 and 1332 are used in a similar manner to thatused above with respect to FIG. 6. The sensors 1330, 1332 may act todetect the tank being drained as well. This may be accomplished in onesensor or two sensors at locations 1330, 1332. Further, two differentdrain ports 44A, 44B are in fluid communication with the drain valves42A, 42B and the respective drain reservoirs 46A, 46B to form drainlines.

In this example, two three-way valves 1310 and 1312 are provided. In asense, the operation of the system is nearly the same as that set forthin FIG. 6B. That is, the low pressure pump 34 fills the tank 40A with aninitial fill of feed water. In state A, the three-way valve 1312 couplesthe port 1314 through valve ports 1312B and 1312C to the high pressurepump 52. The brine outlet pipe 62 is in communication with the port 1318of the tank 40B through valve ports 1310C and 1310A of the valve 1310.The high pressure fluid flow passes through the turbine 74T of theturbocharger 74 to provide boost as described above in FIG. 4. Thepermeate exits the membrane housing 54 through the permeate pipe 58. Thelow pressure brine enters the tank 40B through the port 1318. Over time,the fluid level of the brine in the tank 40B increases while the fluidlevel of the fluid in the tank 40A decreases. To reduce the amount oftime of starting the process, once enough fill fluid has entered thetank 40A, the process may start as long as the filling process is fasterthan the permeate production process. In the same manner described, theconcentrate of the first volume 612 and the second volume 614 aremonitored. Further, the drain valves 42A, 42B act in a similar manner.

Referring now to FIGS. 14A and 14B, once the liquid level of the volume612 in tank 40A is reduced to a substantial amount such as at the bottomof the tank in FIG. 13, the states of the valves 1310 and 1312 switch toa second state in FIG. 14A. That is, valve 1312 communicates fluid fromthe tank 40B through port 1320 to the high pressure pump 52 throughvalve ports 1312A and 1312C. Port 1316 and tank 40A receive fluid fromthe brine pipe 62 through the turbine 74T through valve ports 1310B and1310C. In FIG. 14A, tank 40B is reducing in level while tank 40A isfilling. The high pressure pump 52 will increase the pressure in thefluid to a higher pressure due to the higher total dissolved solids.Once the level of the tank 40B reaches the bottom as indicated by sensor1332, the valves 1310 and 1312 are switched.

Referring now to FIG. 14B, valves 1310 and 1312 are switched to operatein the manner illustrated above with respect to FIG. 13. As can beobserved, the fluid level in tank 40A is reduced from the start of theprocess in FIG. 13. That is, each cycle produces permeate that isremoved from the volume of the tanks. Once the concentration of theremaining brine or the desired amount of permeate has been reduced,drain valves 42A and 42B are open to drain the tanks 40A, 40B. It shouldbe noted that the sensors 1330 and 1332 may act as concentration sensorsor level sensors.

Referring now to FIGS. 15A and 15B, an alternative tank 1510 isillustrated having a common bulkhead 1512. The common bulkhead dividesthe tank 1510 into the first volume 612 and the second volume 614. Acommon outer wall 1514 may surround the entire tank.

Referring now to FIG. 15C, another design for a tank 1550 is set forth.In this example, a first tank 1552 is cylindrical in shape, has volume612 therein and has a longitudinal axis 1554. An outer coaxial tank 1556has volume 614 therein and is disposed around the tank 1552. Of course,other types of designs may be provided. The advantage of providingnested or directly adjacent tanks such as that illustrated in FIGS.15A-15C are the reduced amount of land area required to place the tanks.

Referring now to FIG. 16, the tanks 40A and 40B may be replaced withfabric bags 1610A and 1610B. The fabric bags 1610A, 1610B have ports1612, 1614, 1616 and 1618 that correspond to the ports 1314, 1316, 1318and 1320, respectively, as set forth in FIG. 13. In this example, theports 1612-1616 may be formed of flexible hoses. The bags 1610A and1610B may be floating in water as illustrated by the water line 1620.The fabric bags 1610A, 1610B may be allowed to float in the body ofwater as indicated by the water level 1620 and may be located close to areverse osmosis system in a sheltered bay directly adjacent to thereverse osmosis facility. The bags 1610A, 1610B serve the same functionand hold a first volume 612 and second volume 614, respectively. As thebatch is processed and the brine concentration in the bags increases,negative buoyancy results and thus, subsurface support structures 1630and 1632 may be used to support the fabric bags 1610A and 1610B as thebrine increases.

Referring now to FIG. 17, fabric bags 1610A and 1610B may be used on theland 1650. A sculpted surface 1652 and 1654 may receive bags 1610A and1610B, respectively.

Those skilled in the art can now appreciate from the foregoingdescription that the broad teachings of the disclosure can beimplemented in a variety of forms. Therefore, while this disclosureincludes particular examples, the true scope of the disclosure shouldnot be so limited since other modifications will become apparent to theskilled practitioner upon a study of the drawings, the specification andthe following claims.

What is claimed is:
 1. A reverse osmosis system in communication with afluid reservoir comprising: a membrane housing comprising a reverseosmosis membrane therein, said membrane housing comprising a feed fluidinput, a brine outlet and a permeate outlet; a charge pump; a pluralityof valves; and a first volume disposed in a first bag and a secondvolume disposed in a second bag, wherein said first bag and said secondbag are disposed in a body of water; said plurality of valves operatingso that in a first mode, the charge pump couples a feed reservoir to thefirst volume while the brine outlet and the feed fluid input aresimultaneously connected to the second volume, and in a second mode, thecharge pump is coupling the feed reservoir to the second volume whilethe brine outlet and the feed fluid input are simultaneously connectedto the first volume, wherein the first mode and second mode areconfigured for alternating operation.
 2. The reverse osmosis system ofclaim 1 wherein the plurality of valves are disposed in a spool valve,said spool valve comprises a rod and a plurality of disks coupled to alinear actuator, said linear actuator positioning the disks in a firstposition and thereafter, a second position.
 3. The reverse osmosissystem of claim 2 wherein the spool valve comprises a low pressure end,a high pressure end and a seal between the low pressure end and the highpressure end.
 4. The reverse osmosis system of claim 1 furthercomprising a controller and a concentration sensor generating aconcentration signal corresponding to a salt concentration coupled to adrain line, said controller controlling a flushing of pipes with feedfluid until the salt concentration in the drain line is below athreshold.
 5. The reverse osmosis system of claim 1 wherein the firstbag comprises a first fabric bag and the second bag comprises a secondfabric bag.
 6. The reverse osmosis system of claim 5 wherein the firstfabric bag is disposed adjacent to a sub-surface platform.
 7. Thereverse osmosis system of claim 1 wherein the first bag and the secondbag are disposed in a sculpted surface.
 8. A method comprising: fillinga first volume disposed in a first bag and a second volume disposed in asecond bag, wherein said first bag and said second bag are disposed in abody of water; producing permeate with fluid from the second volume bypassing the fluid through a membrane of a membrane housing, saidmembrane housing comprising a feed fluid input, a brine outlet and apermeate outlet; controlling a plurality of valves so that in a firstmode, a charge pump is coupling a feed reservoir to the first volumewhile the brine outlet and the feed fluid input are simultaneouslyconnected to the second volume, and in a second mode, the charge pump iscoupling the feed reservoir to the second volume while the brine outletand the feed fluid input are simultaneously connected to the firstvolume, wherein the first mode and second mode are configured foralternating operation.
 9. The method of claim 8 wherein controlling theplurality of valves comprises controlling the plurality of valves inresponse to a first volume concentration and a second volumeconcentration.
 10. The method of claim 8 wherein the plurality of valvescomprises a spool valve and wherein controlling the plurality of valvescomprises controlling the spool valve in response to a first volumeconcentration and a second volume concentration.
 11. The method of claim8 further comprising maintaining a constant permeate production rateuntil a concentration of fluid in the second volume reaches a threshold.12. The method of claim 8 further comprising maintaining net drivingpressure until a concentration of fluid in the second volume reaches athreshold.
 13. The method of claim 8 wherein the first bag comprises afirst fabric bag and the second bag comprises a second fabric bag. 14.The method of claim 8 wherein the first bag and the second bag aredisposed in the body of water adjacent to a subsurface supportstructure.
 15. The reverse osmosis system of claim 1 wherein the firstbag and the second bag are disposed adjacent to a sub-surface platform.